Make kernel_map, buffer_map, clean_map, exec_map, and pager_map direct
structural declarations instead of pointers. Clean up all related code,
in particular kmem_suballoc().
Remove the offset calculation for kernel_object. kernel_object's page
indices used to be relative to the start of kernel virtual memory in order
to improve the performance of VM page scanning algorithms. The optimization
is no longer needed now that VM objects use Red-Black trees. Removal of
the offset simplifies a number of calculations and makes the code more
readable.

Further normalize the _XXX_H_ symbols used to conditionalize header file
inclusion.
Use _MACHINE_BLAH_H_ for headers found in "/usr/src/sys/arch/<arch>/include".
Most headers already did this, but some did not.
Use _ARCH_SUBDIR_BLAH_H_ for headers found in "/usr/src/sys/arch/<arch>/subdir"
instead of _I386_SUBDIR_BLAH_H_.
Change #include's made in architecture-specific directories to use
<machine/blah.h> instead of "blah.h", allowing the included header files
to be overrdden by another architecture. For example, a virtual kernel
architecture might include a header from arch/i386/include which then
includes some other header in arch/i386/include. But really we want that
other header to also go via the arch/vkernel/include, so the header files
in arch/i386/include must use <machine/blah.h> instead of "blah.h" for most
of their sub-includes.
Change most architecture-specific includes such as <i386/icu/icu.h> to
use a generic path through the "arch" softlink, such as <arch/icu/icu.h>.
Remove the temporary -I@/arch shim made in a recent commit, the <arch/...>
mechanism replaces it.
These changes allow us to implement heirarchical architectural overrides,
primarily intended for virtual kernel support. A virtual kernel uses an
architecture of 'vkernel' but must be able to access actual cpu-specific
header files such as those found in arch/i386. It does this using a
"cpu" softlink. For example, someone including <machine/atomic.h> in a
vkernel build would hit the "arch/vkernel/include/atomic.h" header, and this
header could then #include <cpu/atomic.h> to access the actual cpu's
atomic.h file: "arch/i386/include/atomic.h".
The ultimate effect is that an architecture can build on another
architecture's header and source files.

Change the kernel dev_t, representing a pointer to a specinfo structure,
to cdev_t. Change struct specinfo to struct cdev. The name 'cdev' was taken
from FreeBSD. Remove the dev_t shim for the kernel.
This commit generally removes the overloading of 'dev_t' between userland and
the kernel.
Also fix a bug in libkvm where a kernel dev_t (now cdev_t) was not being
properly converted to a userland dev_t.

Device layer rollup commit.
* cdevsw_add() is now required. cdevsw_add() and cdevsw_remove() may specify
a mask/match indicating the range of supported minor numbers. Multiple
cdevsw_add()'s using the same major number, but distinctly different
ranges, may be issued. All devices that failed to call cdevsw_add() before
now do.
* cdevsw_remove() now automatically marks all devices within its supported
range as being destroyed.
* vnode->v_rdev is no longer resolved when the vnode is created. Instead,
only v_udev (a newly added field) is resolved. v_rdev is resolved when
the vnode is opened and cleared on the last close.
* A great deal of code was making rather dubious assumptions with regards
to the validity of devices associated with vnodes, primarily due to
the persistence of a device structure due to being indexed by (major, minor)
instead of by (cdevsw, major, minor). In particular, if you run a program
which connects to a USB device and then you pull the USB device and plug
it back in, the vnode subsystem will continue to believe that the device
is open when, in fact, it isn't (because it was destroyed and recreated).
In particular, note that all the VFS mount procedures now check devices
via v_udev instead of v_rdev prior to calling VOP_OPEN(), since v_rdev
is NULL prior to the first open.
* The disk layer's device interaction has been rewritten. The disk layer
(i.e. the slice and disklabel management layer) no longer overloads
its data onto the device structure representing the underlying physical
disk. Instead, the disk layer uses the new cdevsw_add() functionality
to register its own cdevsw using the underlying device's major number,
and simply does NOT register the underlying device's cdevsw. No
confusion is created because the device hash is now based on
(cdevsw,major,minor) rather then (major,minor).
NOTE: This also means that underlying raw disk devices may use the entire
device minor number instead of having to reserve the bits used by the disk
layer, and also means that can we (theoretically) stack a fully
disklabel-supported 'disk' on top of any block device.
* The new reference counting scheme prevents this by associating a device
with a cdevsw and disconnecting the device from its cdevsw when the cdevsw
is removed. Additionally, all udev2dev() lookups run through the cdevsw
mask/match and only successfully find devices still associated with an
active cdevsw.
* Major work on MFS: MFS no longer shortcuts vnode and device creation. It
now creates a real vnode and a real device and implements real open and
close VOPs. Additionally, due to the disk layer changes, MFS is no longer
limited to 255 mounts. The new limit is 16 million. Since MFS creates a
real device node, mount_mfs will now create a real /dev/mfs<PID> device
that can be read from userland (e.g. so you can dump an MFS filesystem).
* BUF AND DEVICE STRATEGY changes. The struct buf contains a b_dev field.
In order to properly handle stacked devices we now require that the b_dev
field be initialized before the device strategy routine is called. This
required some additional work in various VFS implementations. To enforce
this requirement, biodone() now sets b_dev to NODEV. The new disk layer
will adjust b_dev before forwarding a request to the actual physical
device.
* A bug in the ISO CD boot sequence which resulted in a panic has been fixed.
Testing by: lots of people, but David Rhodus found the most aggregious bugs.

device switch 1/many: Remove d_autoq, add d_clone (where d_autoq was).
d_autoq was used to allow the device port dispatch to mix old-style synchronous
calls with new style messaging calls within a particular device. It was never
used for that purpose.
d_clone will be more fully implemented as work continues. We are going to
install d_port in the dev_t (struct specinfo) structure itself and d_clone
will be needed to allow devices to 'revector' the port on a minor-number
by minor-number basis, in particular allowing minor numbers to be directly
dispatched to distinct threads. This is something we will be needing later
on.

kernel tree reorganization stage 1: Major cvs repository work (not logged as
commits) plus a major reworking of the #include's to accomodate the
relocations.
* CVS repository files manually moved. Old directories left intact
and empty (temporary).
* Reorganize all filesystems into vfs/, most devices into dev/,
sub-divide devices by function.
* Begin to move device-specific architecture files to the device
subdirs rather then throwing them all into, e.g. i386/include
* Reorganize files related to system busses, placing the related code
in a new bus/ directory. Also move cam to bus/cam though this may
not have been the best idea in retrospect.
* Reorganize emulation code and place it in a new emulation/ directory.
* Remove the -I- compiler option in order to allow #include file
localization, rename all config generated X.h files to use_X.h to
clean up the conflicts.
* Remove /usr/src/include (or /usr/include) dependancies during the
kernel build, beyond what is normally needed to compile helper
programs.
* Make config create 'machine' softlinks for architecture specific
directories outside of the standard <arch>/include.
* Bump the config rev.
WARNING! after this commit /usr/include and /usr/src/sys/compile/*
should be regenerated from scratch.

DEV messaging stage 1/4: Rearrange struct cdevsw and add a message port
and auto-queueing mask. The mask will tell us which message functions
can be safely queued to another thread and which still need to run in the
context of the caller. Primary configuration fields (name, cmaj, flags,
port, autoq mask) are now at the head of the structure. Function vectors,
which may eventually go away, are at the end. The port and autoq fields
are non-functional in this stage.
The old BDEV device major number support has also been removed from cdevsw,
and code has been added to translate the bootdev passed from the boot code
(the boot code has always passed the now defunct block device major numbers
and we obviously need to keep that compatibility intact).